Arrangement for producing cold at very low temperatures



March 12, 1968 Q p -r ETAL ARRANGEMENT FOR PRODUCING COLL) AT VERY LOW TEMPERATURES- 2 Sheets-Sheet .3

Filed March 21, 1966 AV VN FIG.3

AG NT United States Patent 3,372,554 ARRANGEMENT FOR PRQDUCHNG COLD AT VERY LUW TEMPERATURES Gijsbert Prast, Emmasingel, Eindhoven, Netherlands, as-

signor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 21, 1965, Ser. No. 536,131 Claims priority, application Ngesateherlands, Apr. 6, 1965,

a '7 Claims. (Cl. 62-6) ABSCT OF THE DISCLOSURE A system incorporating two cold gas refrigerators in which the first refrigerator operates at a high pressure and produces cold at a higher mean temperature. The second refrigerator operates at a lower mean temperature and is connected to the first refrigerator whereby the latter makes up for the regenerator losses of the second refrigerator and permits the second refrigerator to achieve low temperatures.

This invention relates to arrangements for producing cold at very low temperatures, for example below 20 K., comprising at least two cold-gas refrigerators each having at least one compression space of variable volume and at least one expansion space likewise of variable volume, and the compression space during operation, having a mean temperature higher than that of the associated expansion space, and the compression and expansion spaces of each machine communicating with one another through at least one regenerator through which a working medium can flow forwards and backwards on its way rom the compression space to the expansion space and vice versa.

If a known cold-gas refrigerator must produce cold at very low temperatures it must operate with very low pressures in view of the non-ideal properties of the working medium at these temperatures, as well as other harmful effects. A multi-space machine as described in Dutch patent specification 90,073 is most suitable for obtaining very low temperatures with only one machine. However, if this machine must operate at very low pressures, its output in the part of higher temperatures becomes very low.

A further arrangement suggested comprises two coldgas refrigerators in which the cold head of the first refrigerator delivers its cold to the compression space of the second cold-gas refrigerator. This arrangement has the disadvantage that the total output is very low.

An object of the invention is to provide an improved arrangement for producing cold at very low temperatures with satisfactory output.

An arrangement according to the invention is characterized in that the cold wall of the expansion space of the first cold-gas refrigerator is connected through heat conduction to an area located in the communication between the compression and expansion spaces of the second coldgas refrigerator, which area is separated from the relevant spaces by regenerators located one on each side thereof, the mean pressure level in the second cold-gas refrigerator being lower than that in the first and the working medium present in the second cold-gas refrigerator having a critical temperature which may be lower than that of the working medium present in the first cold-gas refrigerator.

In the second low-pressure cold-gas refrigerator the compression space is at cooling-Water temperature and the expansion space is at a very low temperature, for example 4 K. The cold produced in a first cold-gas re- 3,3?2,554 Patented Mar. 12, 1968 ice frigerator is used for compensating the regeneration losses occurring in the second refrigerator. It has thus become possible at low pressure in one machine, to produce cold at very low temperatures with a rather satisfactory output. The working media in the two cold-gas refrigerators may then be the same but, according to the invention it is advantageous under certain conditions to use a working medium in the second cold-gas refrigerator which has a critical temperature lower than that of the medium present in the first cold-gas refrigerator. These working media in the second and first cold-gas refrigerators may be H and H respectively.

In a further advantageous embodiment of the arrangement according to the invention, the first cold-gas refrigerator is designed as a multi-space machine.

In relation to the present application, the term multispace machine has to be understood to mean a cold-gas refrigerator having, in addition to a compression space and an expansion space, one or more intermediate expansion spaces located one after another in the communication between the compression and expansion spaces. The first intermediate expansion space communicates through at least one regenerator with the compression space and the final communicates through at least one regenerator with the expansion space. Furthermore, at least one regenerator is provided between each pair of intermediate expansion spaces, the arrangement being such that during operation the expansion spaces which are farther remote from the compression space have temperatures which are lower than those of the nearer spaces.

The second cold-gas refrigerator may be designed as an ordinary two-space machine, an intermediate heat-exchanger being provided somewhere in the middle of the regenerator and being connected in a heat-conductive manner to the cold wall of the expansion space of the first cold-gas refrigerator.

In another advantageous embodiment of the arrangement according to the invention the second cold gas refrigerator is also designed as a multi-space machine in which the wall of that intermediate expansion space which communicates with the expansion space is connected in a heat-conductive manner to the cold wall of the expansion space of the first cold-gas refrigerator.

In another advantageous embodiment of the arrangement according to the invention, in the communication between the compression and expansion spaces of the second cold-gas refrigerator, between the intermediate expansion space connected to the expansion space and the compression space, there is located at least one further area which is connected in a heat-conductive manner to the cold wall of an intermediate expansion space of the first cold-gas refrigerator, and which is bounded by a regenerator on each side. So the working medium of the second cold-gas refrigerator is cooled again, but now at the higher temperature of the intermediate expansion space of the first cold-gas refrigerator. This cold is obtained in a more advantageous manner (higher temperature) than the cold produced in the expansion space (lower temperature) so that this arrangement has a better output. The regenerator losses of the second cold-gas refrigerator are now compensated in a stepwise manner.

Said heat-conductive connections between the relevant areas of the two cold-gas refrigerators may be formed, if desired, by strips or other connections of a material of good thermal conductivity.

In another advantageou embodiment of the arrangement according to the invention, each of said heat-conductive connections is formed by an evaporation-condensation system with a medium having a temperature of condensation which is matched to the temperature of the heat-exchanging area of the firs-t cold-gas refrigerator. The

relevant medium will condense at the heat-exchanging area of the first cold-gas refrigerator and the condensate may be supplied to the heat-exchanging area of the second cold-gas refrigerator, for example, through an insulated system of ducts. The condensate will evaporate again at this area while extracting heat from the working medium. A transport of cold from the first to the second refrigerator is thus obtained which functions in a highly satisfactory manner.

According to the invention the evaporation-condensation system which co-acts with the expansion space of the first cold-gas refrigerator may be filled with hydrogen, Whereas the evaporation-condensation system which coacts with the intermediate expansion space connected to the expansion space is filled with nitrogen. Thus, the cold produced at approximately 20 K. by the first cold-gas refrigerator, is transferred by the hydrogen evaporationcondensation system to the second cold-gas refrigerator. The cold-produced in the intermediate expansion space at the temperature liquid nitrogen is transferred by the nitrogen to the second cold-gas refrigerator.

The arrangement according to the invention permits of producing cold at very low temperatures with a comparatively satisfactory output.

In order that the invention may be readily carried into effect, it will now be described, in detail, by way of example, with reference to the accompanying diagrammatic drawin in which:

FIGURES 1 to 3 show three embodiments of arrange ments for producing cold at low temperatures, each arrangement comprising two cold-gas refrigerators.

The arrangement for producing cold at low temperatures as shown in FIGURE 1 comprises two cold-gas refrigerators A and B. The cold-gas refrigerator A has a piston 1 and a displacer 2 which are connected to a drive mechanism (not shown) through a piston rod 3 and a piston rod 4 respectively. The drive mechanism moves the piston and the displacer with a certain phase difference. The displacer 2 comprises two parts 5 and 6 of different diameters. The piston .1 and the lower side of the displacer during movement vary the volume of a compression space 7. An annular surface 8 formed by the transition between the two parts 5 and 6 of the displacer can vary the volume of an intermediate expansion space 9. The upper side of the displacer part 6 during movement can vary the volume of an expansion space 10. The compression space 7 and the intermediate expansion space 9 communicate with one another through a cooler 11, a first regenerator 12 and an intermediate heat-exchanger 13. The intermediate expansion space 9 and the expansion space communicate with one another through a second regenerator 14 and a second freezer 15. The operation of such a cold-gas refrigerator has been described in the above-mentioned Dutch patent specification 90,073.

The cold-gas refrigerator B is of a similar construction having a piston 21 and a displacer 22 which comprises two parts 25 and 26 of different diameters. In this machine also the piston and the displacer are connected to a drive mechanism (not shown) through a piston rod 23 and a displacer rod 24 respectively. In this refrigerator a compression space 27 communicates through a cooler 31, a regenerator divided into two parts 32 and 32", and an intermediate freezer 33 with an intermediate expansion space 29. The intermediate expansion space communicates through a regenerator 34 and a freezer 35 with an expansion space 30.

The freezer 15 of machine A is connected through a duct to the intermediate freezer 33 of the second machine B. The freezers 15, 33 and the duct 40 contain hydrogen which can condense in the freezer 15 and evaporate in the intermediate freezer 33.

Similarly, the intermediate freezer 13 of machine A is connected through a duct 42 to a heat-exchanger 43 located between the parts 32 and 32" of the regenerator. The freezer 13, the duct 42 and the heat-exchanger 43 contain nitrogen which can condense in the intermediate freezer 13 and evaporate in the heat-exchanger 43.

The cold-gas refrigerator A contains a working medium, for example H at a high mean pressure of, for example, 30 kg./cm. whereas the machine B contains a working medium, for example H at a much lower mean pressure of, for example, 3 kg./cm.

The cold-gas refrigerator A in which the medium is subject to a high mean pressure, produces cold at approximately 70 K. in the intermediate expansion space 9 and produces cold at approximately 20 K. in the expansion space 10.

Since the mean pressure of the medium in the cold-gas refrigerator B is so low, this machine cannot make up for the regenerator losses which occur in the regenerator 32, 32". The cold necessary for compensating these losses is now delivered by the machine A. The cold produced in the intermediate expansion space of the machine A is supplied through the nitrogen evaporation-condensation system to the heat-exchanger 43. The col-d produced in the expansion space 10 is supplied through the hydrogen evaporation-condensation system to the intermediate freezer 33. This intermediate freezer will thus have a temperature of approximately 20 K. Cold can now be produced in the expansion space 30 at a temperature of approximately 4 K. An arrangement is thus obtained which produces cold at 4 K. with a comparatively satisfactory output. As a matter of fact, it is possible also to produce cold at the temperatures prevailing in the intermediate expansion space 9 and the expansion space 10.

Under certain conditions, the duct 42 and the heat-exchanger 43 may be omitted so that only the cold produced at approximately 20 K. in the expansion space 10 is transferred to the intermediate freezer 33. Such an arrangement can also produce cold at approximately 4 K. in a satisfactory manner.

FIGURE 2 shows a slightly different construction of an arrangement for producing cold at very low temperatures. As before, this arrangement comp-rises two coldgas refrigerators A and B. Each cold-gas refrigerator has a displacer which is built up of three parts. In the refrigerator A these are parts 101, 102 and 103, the annular surfaces formed by the transitions of these parts being capable of varying the volumes of expansion spaces 104, 105 and 106. A compression space 107 communicates through a cooler 108, a regenerator 109 and a heat-exchanger 110 with the expansion space 104. This expansion space communicates through a regenerator 111 and a heat-exchanger 112 with the expansion space 105 and the latter communicates through a regenerator 113 and a heat-exchanger 114 with the expansion space 106.

The refrigerator B comprises similar component parts which are indicated in this machine by the reference numerals 201 to 214. The heatexchangers 112 and 114 are connected through ducts 116 and 117 to heat-exchangers 210 and 212 of the refrigerator B. The heat-exchanger 110 is connected through a duct 118 to a heat-exchanging coil 119 in -a regenerator 209.

The cold-gas refrigerator A produces cold in the expansion spaces 104, 105 and 106 at three different temperatures the mean pressure prevailing in this machine being comparatively high. In the cold-gas refrigerator B, the mean pressure is comparatively low so that this machine can no longer make up for the various losses which occur during the passage of the medium through the various regenerators. In order to compensate for these losses, the cold produced in the refrigerator A is transferred to the refrigerator B. This is effected for the cold produced in the expansion 106 by means of hydrogen which condenses in the freezer 114 and then flows through the duct 117 to the heat-exchanger 212, in which the condensate evaporates again while extracting its heat of evaporation from the working medium of the refrigerator B. The same happens with the cold produced in the expansion spaces 105 and 104 which cold is transported to the heat-exchanger 210 and 119. Since the cold is produced in said expansion spaces at a comparatively high temperature, nitrogen is present at a heat-transfer medium in the duct 116 and the associated heat-exchanger and methane or another gas having a corresponding boiling point is present in the duct 118 and the associated heat-exchanger.

Thus an arrangement is again obtained which can produce cold at very low temperatures.

Finally, FIGURE 3 shows another arrangement for producing cold at very low temperatures. This arrangement comprises a three-space cold-gas refrigerator A of the kind shown in FIGURE 1. This machine co-acts with a cold-gas refrigerator D which has only one expansion space. As before, in this arrangement an evaporationcondensation system is formed by a freezer 20, a duct 300 and a heat-exchanger 301 by means of which the cold produced in the expansion space of cold-gas refri erator A is transferred to the working medium of coldgas refrigerator '1). The medium in the refrigerator A is again subject to a comparatively high mean pressure so that this machine produces cold in the expansion space at approximately K. Due to this cold, the hydrogen of the evaporation-condensation system condenses in the freezer 20, whereupon it flows to the heat-exchanger 301 and evaporated therein. Consequently the regeneration losses of the working medium are compensated in the refrigerator D so that this machine can supply cold at the very low temperature of approximately 4 K. despite the fact that the working medium is subject to a comparatively low mean pressure.

From the foregoing it will be evident that the invention provides an arrangement which produces cold at very low temperatures with a comparatively satisfactory output.

What is claimed is:

1. An apparatus for producing cold at temperatures below 20 K. comprising at least two cold gas refrigerators, each having at least one compression space of variable volume and at least one expansion space of variable volume, a working medium in said compression and expansion spaces, said compression space during operation having a mean temperature higher than that of the associated expansion space, and at least one regenerator, and the compression and expansion spaces of each apparatus communicating with one another through said regenerator, said working medium flowing and counterflowing through said regenerator on its way from the compression space to the expansion space and vice versa, a conduit connecting the expansion space of the first cold gas refrigerator to a location in the communication between the compression and expansion spaces of the second cold-gas refrigerator, said location having additional regenerators positioned on either side thereof, the mean pressure level in said second cold-gas refrigerator being lower than that in said first cold-gas refrigerator, and

the working medium in said second cold-gas refrigerator having a critical temperature which is lower than that of the working medium present in said first cold-gas refrigerator.

2. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 1 wherein said first cold-gas refrigerator is with more than one expansion spaces.

3. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 1, wherein said second cold-gas refrigerator is provided with more than one expansion spaces, and the intermediate expansion space which communicates with the expansion space of said first cold-gas refrigerator is connected in a heat conductive manner to said expansion space of said first cold-gas regrigerator.

4. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 3 wherein the communication between the compression and expansion spaces of said second cold-gas refrigerator and the intermediate expansion space connected to the expansion space and the compression space is in heat conductive relationship with the intermediate expansion space of said first coldgas refrigerator, an additional regenerator, said communication being bounded on each side by said additional regenerator.

5. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 1 wherein each of said heat conductive conduits between said first and second cold-gas refrigerators is formed by an evaporation-condensation system provided with a medium having a temperature of condensation which is matched to the temperature of the heat exchanging area of said first refrigerator.

6. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 5 wherein the medium which is present in the evaporation-condensation system connected to the expansion space of said first cold-gas refrigerator is hydrogen.

7. An apparatus for producing cold at temperatures below 20 K. as claimed in claim 5 wherein the medium which is present in the evaporation-condensation system connected to the intermediate expansion space of the first cold-gas refrigerator which communicates with the expansion space is nitrogen.

References Cited UNITED STATES PATENTS 2,48 0,525 8/ 1949 VanWeenen 62-6 2,907,175 10/1959 Kohler 626 3,074,229 1/ 1963 Baas 62-6 3,101,597 8/1963 Dros 6 26 WILLIAM J. WY-E, Primary Examiner. 

